The invention relates to track switch heating arrangements, for example of the type wherein electrical heating elements are arranged on the rail sections of the track switch, with temperature or snow sensors controlling the operation of a regulator which in turn regulates the temperature of the one or more heated rail sections of the track switch.
The expression railway track switch as employed herein is to be understood to refer to switching installations for diverting a locomotive, trolley, or the like, from the track on which it is running to another track, such as a side track or branch track. Track switches include moving track rail sections which move between two positions for effecting the desired routing of the railroad train or the like. It is well known that an accumulation of snow, particularly heavy snow or compacted snow, or ice, can block the movement of the moving track rail sections, or cause other track switch malfunctions. It is accordingly commonly desired to prevent such snow accumulations.
It is already known to provide devices which sense rail temperature or accumulated snow and which are operative for controlling the operation of a track switch heating arrangement. However, the known expedients are characterized by a variety of disadvantages.
If the temperature or snow sensors are operative independently of the temperature of the track rail sections of the track switch, or independently of the actual accumulation of snow on the switch, they have the disadvantage that, after effecting initiation of the heating of the track rail section of the track switch, they do not with similar quickness terminate such energy-consuming heating. In the case of temperature sensors, for example, a considerable time may elapse between the rise of the track rail section to an acceptable temperature and a similar temperature rise of the sensor. In the case of snow sensors, the heating may have melted the snow capable of interfering with track switch operation long before the snow in the vicinity of the sensor melts. Furthermore, such sensors may not effect initiation of heating of a track rail section when such heating is required. For example, on a day when the temperature is sub-freezing, a snow-covered train arriving from a locality where a snowfall has occurred may dump a considerable amount of snow or ice upon a track switch in a locality where no snowfall has occurred, due to the forceful vibration of the train as it passes over the track switch, with the result that the track switch becomes covered over or clogged with compacted snow or ice although no snow reaches the snow sensor. There are other reasons why the height of the snow detected by the sensor may not correspond accurately enough to the snow accumulation on the track switch.
Accordingly, it has already been proposed to locate a temperature sensor, such as a semiconductor, a thermoelement, or the like, in contact with a track rail section of the track switch in the region of the moving track rail section of the switch, and to furthermore provide the temperature sensor with its own regulating circuit for the heating current, all in a single housing.
Electronic snow sensors, compared to temperature sensors, have the advantage that they respond faster and more directly to the presence of snow. However, when used in the context in question, known snow sensors do not operate in a completely satisfactory manner. Those which operate upon the basis of a resistance change between two electrodes, and also those which operate upon the basis of a change in the inductance of a sensing coil, undesirably respond not only to snow but also to dirt, dust and the like, and accordingly must be arranged outside the vicinity of the track switch at some height above the level of the ground.